The representation of the edge of a spectacle lens is understood by the disclosure to mean a representation of the bearing edge of the spectacle lens constituted in the standard EN ISO 13666:2012 (D/E), section 13.1.
A representation of the edge of a spectacle lens is a dataset, from which the three-dimensional curve of the bearing edge of the spectacle lens facing away from the spectacle wearer can be determined unequivocally as appropriate on the basis of additional variables describing the spectacle lens. A representation of the edge of a spectacle lens can, for example, be the area surrounded by the projection of the edge of the spectacle lens in the image plane of an image sensor of an image capture device, into which area the spectacle lens is projected for the image capture.
In the case of fully rimmed spectacles, the bearing edge of a spectacle lens corresponds to an inner edge of the spectacle frame. In the case of partially rimmed spectacles, the bearing edge of a spectacle lens is understood on the one hand to mean the edge of a spectacle lens corresponding to the inner edge of the spectacle frame and the lens outer edge not adjoining the spectacle lens frame. The bearing edge of a spectacle lens in the case of rimless spectacles is the lens outer edge.
To fit the spectacle lenses correctly into a spectacle frame, it is necessary on the one hand to determine so-called centering parameters, so that the optical centers of the lenses can be brought into alignment with the visual axes of the corresponding eyes, in order thus for example to acquire information concerning the pupil distance and information concerning the height of the pupils in relation to the spectacle frame. On the other hand, it is necessary to know the bearing edge of the spectacle lens defined by the spectacle frame, in which spectacle frame the spectacle lens is to be received.
Apart from information concerning the pupil distance and information concerning the height of the pupils in relation to the spectacle frame, the following variables in particular are included under the term centering parameter: monocular pupil distance PD, corneal vertex distance HS according to reference point requirement and/or according to ocular pivot point requirement, monocular centration distance, centering point coordinates, lens distance, decentration of the centering point, lens height and width, lens center distance, spectacle lenses angle α, frame lens angle β, and fitting height.
The centering parameters are usually determined by an ophthalmic optician. Important centering parameters are defined for example in standard EN ISO 13666:2012 (D/E) and can be established by an optician and a subject standing or sitting opposite one another, wherein the subject puts on the frame of his choice with a spectacle lens received therein. The subject is asked to look into the distance, and the optician then draws on the lens or a ruled contact film, based on his visual judgement, a cross at the viewing reference point, which he has sighted from his visual reference opposite the subject. This cross (centering cross) then determines the position of the optical center-point of the spectacle lens to be used in the frame. This method is performed separately for each of the subject's eyes. The distance of the centering cross thus established is the pupil distance PD.
For the centering parameter determination, however, automated measurement systems are nowadays also used. Such a measurement system is described for example in WO 01/84222 A1. This system contains a digital video camera accommodated in a height-adjustable manner in a column, the objective lens whereof is arranged together with a mirror and a light source in the region of the front face of the housing. In particular, the system enables the measurement of distances and the capturing of dimensions, which have to be taken into account for the grinding-in of spectacle lenses. In this system, there is a computer connected to the digital video camera, which determines centering parameters for the spectacle frame by means of image evaluation from the image of a spectacle wearer with a spectacle frame and with a measuring bracket fixed to the spectacle frame.
For an ophthalmic optician who is advising end customers, it is important that the centering parameter determination can be carried out as easily, quickly, and reliably as possible. In order that the ophthalmic optician can provide the end customers with high-quality advice, workflows are therefore of interest that are inherently free from error and can be carried out quickly.
In D. Borza et al., “Eyeglasses Lens Contour Extraction from Facial Images Using an Efficient Shape Description,” Sensors, vol. 13, no. 10, pages 13638 to 13658 (2013), a computer-implemented method of the type mentioned at the outset is described for the determination of the edge of spectacle lenses in a captured image of a spectacle wearer, wherein the number of points of the image points lying on the edge of the spectacle lenses is modelled as a superposition of mathematical functions based on the definition of so-called Fourier descriptors.
These mathematical functions describe different spectacle rim shapes. The functions used here for the modelling of the edge of spectacle lenses are stochastic, i.e., are selected according to a random principle from an infinite number of possible functions. The model for the edge of the spectacle lenses described on the basis of the selected functions is stochastic, i.e., selected according to a random principle from an infinite number of possible functions. The model for the edge of the spectacle lenses described on the basis of the selected functions is then compared with a spectacle lens edge established in an edge detection process and evaluated.
In C. Nieuwenhuis et al., “Spatially Varying Color Distributions for Interactive Multi-Label Segmentation, IEEE Transactions on Pattern Analysis and Machine Intelligence,” IEEE Computer Society, USA, vol. 35, no. 5, pages 1234 to 1247 (2013), a method for the segmentation of different regions in digital images is described. Here, the color of image points in the digital images is evaluated. For this purpose, an operative manually marks on a computer different image regions which are to be segmented, for example with a computer mouse. The different image regions are then segmented by optimization of a cost function based on conditional probabilities. For this, the conditional probability that the image point lies in a specific image region is maximized for each image point in the images on the basis of the color information in respect of the manually marked image regions. At the same time, the segmented regions are intended to be as compact as possible.
A. Fernandez et al., “Glasses detection on real images based on robust alignment, Machine Vision and Applications,” Springer Verlag, vol. 26, no. 4, pages 519 to 531 (2015), discloses a method for evaluating photographs of persons to identify whether the persons are spectacle wearers. This method detects unchanging facial features and calculates therefrom the region around the eyes. Within this region, a feature vector by means of which the person is classified as wearer of spectacles or non-wearer of spectacles is determined from the colors.
C. Wu et al., “Automatic Eyeglasses removal from Face Images,” IEEE Transactions on Pattern Analysis and Machine Intelligence, IEEE Computer Society, USA, vol. 26, no. 3, pages 332 to 336 (2004) discloses a method which is used for removing spectacles and spectacle lenses from digital shots of people. The method learns from a database, in which people with and without spectacles are stored, how the eye region has to be altered to remove the spectacles from the face. Moreover, the contour of the frame can be detected by optimizing points on the edge of the frame and external parameters such as rotation, scaling and translation by means of a stochastic method.
DE 10 2011 115 239 A1 describes, in a digital image of a spectacle wearer, how to establish the contour of the edge of the spectacle lenses using a spectacle lens-specific tracer dataset, which contains the curve of the spectacle lens edge.